1. Field of the Invention
The present invention relates to a method and apparatus for preparing variable density drilling muds and completion fluids. The present invention particularly relates to a method and apparatus for preparing variable density drilling muds for use on offshore drilling rigs.
2. Background of the Art
Drilling for oil and gas in very deep water presents problems not found in terrestrial or shallow water oil and gas exploration. One problem encountered in deep water is drilling fluid management. A drilling fluid is a fluid specially designed to be circulated through a wellbore as the wellbore is being drilled to facilitate the drilling operation. The circulation path of the drilling fluid typically extends from the drilling rig down through the drill pipe string to the bit face and back up through the annular space between the drill pipe string and wellbore face to the wellhead and/or riser, returning to the rig. The drilling fluid performs a number of functions as it circulates through the wellbore including cooling and lubricating the drill bit, removing drill cuttings from the wellbore, aiding in support of the drill pipe and drill bit, and providing a hydrostatic head to maintain the integrity of the wellbore walls and prevent well blowouts. The drilling fluid also desirably prevents sloughing and wellbore cave-ins when drilling through water sensitive formations.
There are a number of different types of conventional drilling fluids including compositions termed xe2x80x9cdrilling muds.xe2x80x9d Drilling muds comprise high-density dispersions of fine solids in an aqueous liquid, which is usually brine, or a hydrocarbon liquid. An exemplary drilling mud is a dispersion of clay and/or gypsum in water. The solid component of such a dispersion is termed a xe2x80x9cweighting agentxe2x80x9d and is designed to enhance the functional performance of the drilling fluid.
For the purposes of the present invention, a brine is an aqueous solution of sodium chloride or calcium chloride. Preferable, the brine is near saturation, but the term brines also include more dilute solutions, including but not limited to seawater.
In shallow water drilling, a riser system, that is a separate casing rising from the sea floor to the base of a drilling ship or drilling rig, can be used to return drilling mud to a drilling ship or platform for reuse. The use of a riser is not without problems, and these problems can be exaggerated in deep water drilling projects. One such problem is weight. A 6,000-foot riser 21 inches in diameter holding drilling mud has been estimated to weigh from about 1,000 to 1,500 tons. It is for this reason that riserless drilling methods have beer disclosed, particularly for deep water drilling, in patents such as U.S. Pat. No. 6,102,673 to Mott, et al., and U.S. Pat. No. 4,149,603 to Arnold.
Another problem encountered in offshore drilling is space. On either a drilling ship or a drilling platform, the tools essential to drilling a well require a lot of space. For example, to drill a well requires a drilling apparatus that includes motors and hoists and the like. Also needed for drilling a well are pumps, pipe, drilling fluids, casings, fuel, and living space for a crew. As with any construction project involving a ship or drilling platform, it generally costs more to build larger. It is for this reason that drilling ships and platforms are built no larger than necessary and any new process for such a venue is desirably not space intensive. It is also desirable in the art of drilling oil and gas wells using drilling ships and platforms to improve existing processes to require less space.
Yet another problem with offshore drilling is logistics. Since there are no roads or rail service to offshore installations, pipe, drilling mud, drill bits, personnel, fuel, and the like must all be delivered by means of boats or helicopters. While there is a service industry that provides such services, the modes of transportation are more expensive than truck or rail transportation and more difficult schedule. Therefore, it would be desirable in the art of drilling offshore oil wells to reduce volume of consumable supplies needed to drill an oil well.
In one aspect, the present invention is an apparatus for preparing variable density drilling muds comprising a mixing chamber, a first and a second feed line serving the mixing chamber, the first feed line having a first flow meter and a first control valve therein, and the second feed line having a second flow meter and a second control valve therein, wherein at least one of the flow meters is responsive to a nonintrusive sensory mechanism.
In another aspect, the present invention is a method of preparing variable density drilling muds comprising feeding water and a high-density base fluid to an apparatus for preparing variable density drilling muds, the apparatus comprising a mixing chamber, a first and a second feed line serving the mixing chamber, the first feed line having a first flow meter and a first control valve therein, and the second feed line having a second flow meter and a second control valve therein, wherein at least one of the flow meters is responsive to a nonintrusive sensory mechanism.
In still another aspect, the present invention is a portable apparatus for preparing variable density drilling mud comprising an apparatus for preparing variable density drilling muds, the apparatus comprising a mixing chamber, a first and a second feed line serving the mixing chamber, the first feed line having a first flow meter and a first control valve therein, and the second feed line having a second flow meter and a second control valve therein, wherein at least one of the flow meters is responsive to a nonintrusive sensory mechanism, wherein the mixing chamber and other elements are sized to fit into a rectangular form having dimensions of about 4 feet by 4 feet by 2 feet and further comprising a frame to hold apparatus elements, a means for attaching the frame to the deck of a ship or drilling rig, and quick couplings for attaching the feed lines to hoses having compatible couplings.